1. Field of the Invention
The present invention relates to a milling apparatus incorporated in an adhesive book binding system executing a series of adhesive book binding process while conveying a sheet bundle.
2. Description of the Related Art
As shown in FIGS. 4 and 5, a conventional adhesive book binding system 1 includes a sheet bundle receiving section 2, a milling section 3, a bonding section 4, and a book cover attaching section 5. The adhesive book binding system 1 is configured to sequentially convey a sheet bundle 16 received at the sheet bundle receiving section 2 to each of the sections while clamping it by a clamper 6, thereby executing respective adhesive book binding processes.
The sheet bundle receiving section 2 receives the sheet bundle 16 formed by stacking sheets 15 supplied from a printer or a copier, etc. according to page number. In the sheet bundle receiving section 2, the sheet bundle 16 is clamped between a movable unit 7 and a fixed unit 8 of the clamper 6 in such a manner that the spine 16a of the sheet bundle 16 faces to a level plate 9 positioned under the clamper 6.
A milling apparatus 30 is arranged in the milling section 3. The milling apparatus has a disc-shaped milling cutter 31, and a drive apparatus 32 rotationally driving the milling cutter 31. The milling cutter 31 is provided with a large number of trimming blades 31a upwardly protruding from an outer periphery thereof, as shown in FIGS. 7A and 7B. The milling cutter 31 has groove cutting blades 31b or 31c upwardly protruding from an inner side in a radial direction thereof. The sheet bundle 16 passes through an upper side of the rotating milling cutter 31 with its spine 16a directed downward, whereby the spine 16a is trimmed by the trimming blades 31a, and grooves for adhesive bonding 16b or 16c are formed by the grove cutting blades 31b or 31c. 
In the bonding section 4, an adhesive bonding by a bonding unit 11 is executed for the spine 16a of the sheet bundle 16 in which the grooves for adhesive bonding 16b or 16c are formed by the milling section 3.
In the book cover attaching section 5, a book cover 17 is fed onto nip plates 12 and 13 from a book cover storage (not shown), and is positioned at a predetermined position. The bonded sheet bundle 16 is placed on the positioned book cover 17. The book cover 17 is adhered to the spine 16a of the sheet bundle 16 by an ascent of the nip plates 12 and 13 and a bottom plate 14. At the same time, the spine 16a of the sheet bundle 16 is pressed firmly on both sides by a movement of the nip plates 12 and 13 coming close to each other. Accordingly, the book cover 17 is bent along the sheet bundle 16.
As an adhesive for binding the spine 16a of the sheet bundle 16, an ethylene vinyl acetate (EVA)-based hot melt adhesive is used generally. The EVA-based hot melt adhesive has an ethylene vinyl acetate copolymer as a raw material. Since the EVA-based hot melt adhesive can be repeatedly melted and cured, the EVA-based hot melt adhesive is easily handled and is excellent in a workability. However, the EVA-based hot melt adhesive has week adherence. Therefore, when using the EVA-based hot melt adhesive, as shown in FIGS. 6A and 7A, deep grooves 16b formed at a relatively coarse pitch are required on the spine 16a of the sheet bundle 16.
On the other hand, it is possible to a polyurethane reactive (PUR)-based hot melt adhesive as an adhesive for binding the spine 16a of the sheet bundle 16. Since the PUR-based hot melt adhesive does not melt again once it has cured, it is not easy to deal with the PUR-based hot melt adhesive. However, the PUR-based hot melt adhesive achieves a strong adherence when the reaction is finished. Therefore, when using the PUR-based hot melt adhesive, unlike the EVA-based hot melt adhesive, it is not necessary to form the deep grooves. In other words, when using the PUR-based hot melt adhesive, shallow grooves 16c as shown in FIGS. 6B and 7B are formed at a relatively fine pitch on the spine 16a of the sheet bundle 16.
Therefore, when forming the shallow grooves 16c, it is required to provide a milling apparatus 30 having a rotating shaft 31d of the milling cutter 31 tilted with respect to a conveying direction of the sheet bundle 16, as shown in FIG. 7B. Otherwise, the shallow grooves 16c formed in an upstream side in the conveying direction are again cut in a downstream side and lost.
On the contrary, the deep grooves 16b for the EVA-based hot melt adhesive are not necessarily formed at a fine pitch. Therefore, when forming the deep grooves 16b for the EVA-based hot melt adhesive, it is required to provide a milling apparatus 30 having a rotating shaft 31d of the milling cutter 31 approximately orthogonal to the conveying direction of the sheet bundle 16, as shown in FIG. 7A.
In other words, in order to selectively use the EVA-based hot melt adhesive and the PUR-based hot melt adhesive in the same adhesive book binding system, both the milling apparatus for forming the deep grooves and the milling apparatus for forming the shallow grooves are required. As a result, there is a problem that a space occupied by the milling apparatus is increased, and the adhesive book binding system becomes large in size.